The present invention relates to a method of counting articles, and more particularly to a method of counting articles by finding the total weight of articles contained in a plurality of weighing hoppers, dividing the total weight by the unit weight of the article to determine the number of articles in each weighing hopper, selecting a combination of those weighing hoppers containing a number of articles which is equal to or closest to a target number within a preset allowable range, and discharging the articles from the selected weighing hoppers.
It is generally quite cumbersome to count small articles such as bolts, nuts and the like. Counting such articles one by one is tedious and time-consuming as they normally need to be counted in a large quantity. There has been used an article counting apparatus for weighing a multiplicity of articles to determine their total weight and dividing the total weight by the unit weight of the article to find the number of the articles. Such an article counting apparatus operates by measuring the total weight of a number of articles contained in each of a plurality of weighing hoppers, dividing the weight by the unit weight of the article to find the number of articles in each weighing hopper, selecting a combination of those weighing hoppers which contain a total number of articles that is closest to a target number of articles within a preset allowable range, and discharging the articles from the selected weighing hoppers. Thereafter, the weighing hoppers from which the articles have been removed are replenished with new articles to be weighed so as to be ready for an operation to find a next combination of weighing hoppers. The foregoing process is then repeated for continued automatic counting of articles. FIG. 1 illustrates the general construction of such an article counting apparatus. The article counting apparatus has a dispersing table 11 of the vibratory conveyance type for vibratably dispersing articles radially outwardly when the dispersing table 11 is vibrated for a predetermined interval of time. The articles thus radially outwardly dispersed are supplied into a plurality of n radial weighing stations 1, 1, . . . disposed around the dispersing table 11. Each weighing station 1 includes a dispersing feeder 1a, a pool hopper 1b, a pool hopper gate 1c, a weighing hopper 1d, a weight sensor 1e, a weighing hopper gate 1f, and a hopper driver unit 1g.
As shown in FIG. 2, the dispersing feeder 1a is composed of a feeder base 1a-1 and a trough 1a-2 mounted on the feeder base 1a-1 with an electromagnetic feeder 1a-3 and a leaf spring 1a-4 interposed therebetween. A multiplicity of such feeder bases 1a-1 are arranged radially outwardly around the outer circumference of the dispersing table 11 and mounted by coil springs 1a-5 on a circular support base 1h positioned above a frame of the article counting apparatus. When articles are supplied onto the dispersing table 11 which is imparted with spiral reciprocable motion by an electromagnetic vibratory unit, the articles are discharged radially outwardly off a conical surface of the dispersing table 11 under such spiral reciprocable motion and supplied into the troughs 1a-2. The articles thus supplied into the troughs 1a-2 are then conveyed in the direction of the arrow (FIG. 2) in the troughs 1a-2 upon rectilinear reciprocable movement of the electromagnetic feeder 1a-3, and fall off the distal end of the troughs into the respective pool hoppers 1b. In FIG. 1, the pool hopper gate 1c is provided on each pool hopper 1b in such a manner that the articles received in the pool hopper 1b are released into the weighing hopper 1d when the pool hopper gate 1c is opened under the control of the corresponding hopper driver unit 1g. Each weight sensor 1e, accompanying a respective one of the weighing hoppers 1d, is operable to measure the weight of the articles introduced into the corresponding weighing hopper, and to apply an electrical signal indicative of the measured weight to a combination control unit (not shown). The combination control unit serves to divide the weight of articles contained in each of the weighing hoppers by the unit weight of the article to determine the number of articles in each weighing hopper, and then serves to select an optimum combination of those weighing hoppers which contain a total number of articles that is closest to a target number.
Each weighing hopper 1d is provided with its own weighing hopper gate 1f. Only the weighing hopper gates 1f of the weighing hoppers in the optimum combination are opened under the control of the hopper driver unit 1g to discharge the articles into a common chute 1j wherein they are collected together. The collecting chute 1j has the shape of a funnel and is so arranged as to receive the articles from any of the circularly arrayed weighing hoppers via the hopper gages, which are located above the funnel substantially along its outer rim. The articles received by the collecting chute 1j are collected at the centrally located lower end thereof by falling under their own weight or by being forcibly shifted along the inclined wall of the funnel by a mechanical scraper or the like (not shown).
In operation, articles are charged into each of the pool hoppers 1b and weighing hoppers 1d. The weight sensors 1e associated with the weighing hoppers 1d measure the weights of the articles and supply the combination control unit (not shown) with signals indicative of the measured weight values, denoted L.sub.1 through L.sub.10. The combination control unit computes the numbers of articles contained respectively in the weighing hoppers based on the weight values L.sub.1 through L.sub.10, and selects an optimum combination of those weighing hoppers which contain a total number of articles that is closest to a target number within a preset allowable range. The hopper driver units 1g respond by opening the prescribed weighing hopper gates 1f based on the optimum combination, whereby the articles giving the optimum combination are released into the collecting chute 1j from the corresponding weighing hoppers 1d. This will leave the selected weighing hoppers 1d empty. Subsequently, therefore, the pool hopper gates 1c corresponding to the empty weighing hoppers 1d are opened to introduce a fresh supply of articles from the respective pool hoppers 1b into the weighing hoppers 1d, leaving these pool hoppers 1b empty. Accordingly, the dispersing feeders 1a which correspond to the empty pool hoppers 1b are vibrated for a predetermined period of time to deliver a fresh supply of articles to these empty pool hoppers 1b. This restores the weighing apparatus to the initial state to permit resumption of the control operation for selecting the optimum weight combinations in the manner described. Thus, counting by the article counting apparatus may proceed in continuous fashion by repeating the foregoing steps.
The articles to be counted by the article counting apparatus are such that not all of the articles have equal unit weights, but the actual unit weights of the articles may differ slightly from a reference unit weight. When there is a difference between the preset unit weight and the actual unit weight of the article, the computed number of articles contained in each weighing hopper is subjected to an error, with the result that the number of combined articles which has been computed by adding the articles in the selected weighing hoppers is also subjected to an error. Accordingly, the articles cannot always be counted accurately. Another problem is that the greater the number of articles to be counted by a single weighing machine, the greater the error the computed number of articles has. Correct computation of the number of a multiplity of articles, therefore, requires that the unit weights of the articles be determined correctly. Since articles vary in weight, however, it is meaningless to find unit weights by weighing individual articles correctly. It is better practice to weigh a multiplicity of articles and divide their total weight by the number of the articles to determine average unit weight. The greater the number of articles to be weighed, the more correctly the unit weight can be obtained.
The assignee of the subject application has proposed an article counting apparatus wherein unit weights are automatically variable as disclosed in Japanese Patent Application No. 55-133908. According to this proposal, the article counting apparatus operates by weighing a multiplicity of articles with n weighing machines, dividing the total weight measured by each weighing machine by the unit weight of the article to find the number of articles contained in each of the weighing machines, then computing various combinations of articles to determine the numbers of articles thus combined, and finding one of the combinations which has the number of articles equal or closest to a preset number. The article counting apparatus then computes a new unit weight based on the total weight of articles contained in a single or a plurality of weighing machines and the total number of articles contained in said single or plurality of weighing machines, and relies on the new unit weight in a next counting operation for computing the number of articles.
Where articles such as bolts, nuts or the like are to be counted which have only slightly different actual unit weights, there are instances in which it is better not to renew the unit weight determined in each article counting operation. More specifically, where article unit weights vary only slightly and are subject to a gradual change, no large unit weight difference results when the unit weight is renewed each time the articles are counted. Therefore, the computation process is rendered useless.
When the unit weight suffers from a large difference for some reasons and it is renewed into a new unit weight which differs widely from the previous one, there is a tendency for a next counting operation to fail to count the articles correctly, or for the unit weights of the discharged articles to differ eventually.